B6J.129S1-Htt^tm1Mfc/190ChdiJ

Stock number: 027410
Product name: B6J.zQ175 KI ; Q175 Knock-In (wt x het) ; CHDI-81003003
Research areas: Neurobiology Research, Research Tools

Description

The zQ175 knock-in (zQ175 KI) allele has the mouse Htt exon 1 replaced by the human HTT exon 1 sequence with a ~190 CAG repeat tract (see note below). These B6J.zQ175 KI mice (Stock No. 027410) are useful for studying Huntington's disease pathogenesis and for the assessment of potential therapeutic interventions.
This zQ175 KI allele is the same design as the zQ175 neo-deleted knock-in allele (zQ175DN KI; Stock No. 029928), with the exception that this zQ175 KI retains the floxed neo cassette. It is not specifically characterized if deletion of the neo cassette alters the zQ175DN KI phenotype compared to the zQ175 KI phenotype.

As of November 2017, the Stock No. 027410 live colony has 180-220 CAG repeats.

Detailed description

Stock No. 027410 was formerly associated with CHDI Foundation colony Stock No. 370476 [CHDI-81003003].

The phenotype description below is for zQ175 KI mice with ~190 CAG repeat length. Importantly, as of November 2017, the Stock No. 027410 live colony has 180-220 CAG repeats.
Huntington's disease (HD) is an autosomally dominant, fatal neurodegenerative disorder characterized by uncontrolled movements, psychiatric disturbances and cognitive impairment. HD is caused by an unstable trinucleotide (CAG) repeat expansion in the huntingtin gene (HTT; HD or Hdh).
The zQ175 knock-in (zQ175 KI) allele replaces mouse Htt exon 1 with the human HTT exon 1 sequence with ~190 repeats of a pure CAG tract [(CAG)nCAACAG, encoding polyglutamine]. The CAG repeat number is subject to germline and somatic instability, and may expand or contract. zQ175 mice have mutant mouse/human chimeric protein expression in brain at similar levels of normal endogenous huntingtin protein. Homozygous and heterozygous mice are viable and fertile with some characteristics that phenocopy Huntington's disease. Homozygous mice exhibit weakened grip strength (~4 weeks of age), motor deficit (~8 weeks of age), impaired rotarod and climbing activity (~30 weeks of age), circardian rhythm disruption (~9 months of age), cognitive deficits (~1 year of age), operant learning deficits (~1 year of age) and significantly reduced survival (median ~90 weeks of age). In addition, homozygous mice have huntingtin inclusions/aggregates (~2-4 months of age), early and significant decreased striatal gene markers (from ~12 weeks of age) and decreased neuronal cell counts. Heterozygous mice show behavioral deficits from around 4.5 months of age, especially in the dark phase of the diurnal cycle. Heterozygous mice also show motivational deficits (~30 weeks of age) and operant learning deficits (~1 year of age). Decreased expression of striatal gene markers are detected in heterozygous mice from ~18 weeks of age. Both heterozygotes and homozygotes have decreased body weight (from ~8 weeks of age).

This zQ175 KI allele (Stock No. 027410) is the same design as the zQ175 neo-deleted knock-in allele (zQ175DN KI; Stock No. 029928), with the exception that this zQ175 KI retains the floxed neo cassette. It is not specifically characterized if deletion of the neo cassette alters the zQ175DN KI phenotype compared to the zQ175 KI phenotype.

This Huntington's disease mouse model is available by way of a collaborative effort between CHDI Foundation, Dr. Scott Zeiltin (University of Virginia), Dr. Marie-Francoise Chesselet (University of California, Los Angeles), PsychoGenics, Inc. and The Jackson Laboratory.

In these mutant mice, the CAG repeat number is subject to germline and somatic instability, and may expand or contract. When using lines with unstable CAG repeat length, it is strongly recommended the CAG repeat number be quantified in all the experimental animals; all animals in all experimental groups should carry comparable CAG repeat sizes. CAG repeat sizing of HD mice should be done using high-resolution methods; as assays based on agarose gel electrophoresis typically do not provide sufficient resolution to accurately measure CAG repeat numbers. If labs do not have access to the appropriate equipment for determining CAG repeat length, CAG repeats can be evaluated on a fee-for-service basis by Laragen, Inc.

Development

The zQ175 knock-in (zQ175 KI) allele was derived from a spontaneous expansion of the CAG copy number in CAG140 knock-in (CAG 140 KI) mice as described below. The zQ175 knock-in (zQ175 KI) mouse was generated by Drs. Scott Zeitlin (University of Virginia) and Marie-Francoise Chesselet (University of California, Los Angeles) and colleagues. A fragment extending from 18 bp upstream of huntingtin (Htt; HD or Hdh) exon 1 to 100 bp into intron 1 was replaced with human HTT sequence containing 140 repeats of a pure CAG tract [(CAG)nCAACAG, encoding polyglutamine]. A floxed neo cassette was retained 1.3 kbp upstream of exon 1. The targeting vector was microinjected into 129S1/Sv-Oca2⁺ Tyr⁺ Kitl⁺-derived W9.5/W95 embryonic stem (ES) cells. While backcrossing onto C57BL/6J at PsychoGenics, germline expansions of the CAG tract led to the identification of a mouse with 175 CAG repeats. This mouse was selectively bred to create a new subline, named zQ175 (with the letter z used to identify that the line was derived from a line created by Scott Zeitlin). Subsequently, the CAG repeat number in zQ175 expanded further, and a line was selectively stabilized with ~190 CAG repeats.

This line is identical in construct to CAG 140 KI mice except for CAG tract size.

The zQ175 KI mice have been backcrossed with C57BL/6J inbred mice (Stock No. 000664) five or more generations to create the C57BL/6J-congenic colony (B6J.zQ175 KI), called CHDI Foundation colony Stock No. 370476 [CHDI-81003003].

In 2014, heterozygous animals with ~190 CAG repeat length were sent from the CHDI Foundation colony to The Jackson Laboratory Repository, from which B6J.zQ175 KI heterozygotes are available as Stock No. 027410.

As of November 2017, the Stock No. 027410 live colony has 180-220 CAG repeats.

Allele

Symbol: Htt^tm1Mfc
Name: targeted mutation 1, Marie-Francoise Chesselet
MGI accession ID: MGI:2675580
Generation method: Targeted
Attributes: Humanized sequence
Marker symbol: Htt
Marker name: huntingtin
Chromosome: 5
Strain of origin: 129S1/Sv-Oca2⁺ Tyr⁺ Kitl⁺
Molecular note: A fragment extending from 18 bp upstream of the polyglutamine stretch in exon 1 to 100 bp into intron 1 was replaced with human HD sequence containing 140 CAG repeats. A floxed neo cassette was retained 1.3 kb upstream of exon 1. Western blot analysis of homozygous mutant cerebellum and forebrain tissues identified protein corresponding with the mouse/human hybrid protein. Similar levels of mutant and endogenous protein were observed. The repeat number is not stable and may expand or contract.